Employee Bargaining Agreements and Benefit Plans - Assumption Rates Used for Net Periodic Benefit Costs (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Discount rate:		2.50%	2.70%
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate:	2.65%
Expected return on assets:	3.02%	3.10%	3.27%
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate:	2.90%
Expected return on assets:	3.62%	4.17%	4.27%